The present invention relates to a catalyst for preparing an ultra high molecular weight polyethylene (UHMWPE) and also a method for preparing a UHMWPE with the use of that catalyst, and particularly relates to a solid complex titanium catalyst supported by a carrier containing magnesium for production of UHMWPE along with a preparation method by the use of that catalyst, of a UHMWPE with a large bulk density and narrow particle distribution with few untowardly large or small particles.
UHMWPE, a sort of polyethylene resin, having a molecular weight of at least 10 g/mol or more, and, according to ASTM 4020, is defined as xe2x80x9clinear polyethylene having a relative viscosity of 2.30 or more when measured in 100 ml of 0.05% decahydronaphthalene solution at 135xc2x0 C.xe2x80x9d Because UHMWPE has a larger molecular weight than the polyethylene for ordinary use, it has excellent characteristics in strength, wear resistance, self-lubricating ability, chemical resistance, and electrical properties. Owing to these excellent properties, UHMWPE can be considered a special raw material having high quality obtained from a common raw material.
UHMWPE prepared by the process of polymerization is so large in molecular weight it can not be prepared in pellets, as is the case for ordinary polyethylene, but in powder for commercial use. In powder form, the size and distribution of the polymer powders should be considered important. Thus the particle size distribution of the polymer, and the existence or absence of minute particles are the decisive factors for the quality of the catalyst used.
A magnesium-containing catalyst, based on titanium, for the preparation of UHMWPE and its manufacturing process have been reported. A method making use of a magnesium solution intended to obtain a catalyst for polymerization of olefin having high bulk density has also been learned. U.S. Pat. No. 4,962,167 has disclosed the process of preparing a catalyst obtained by reacting what has been produced by reaction of a magnesium halide compound and a titanium alkoxide compound on one hand with what has been obtained by reaction of an aluminum halide and a silicon alkoxide compound on the other. The catalyst thus prepared provides a polymer of relatively high bulk density, but has to be improved, not to say the problems in the catalytic activity.
U.S. Pat. No. 5,587,440 disclosed a preparation method for a polymer with a narrow particle size distribution and a high bulk density by reducing a titanium(IV) halide to an organic aluminum compound and subjecting it to a post-treatment process, but this product has a demerit of relatively low catalytic activity.
As has been examined above, a preparation method for a catalyst with high polymerization activity to produce an UHMWPE having a high bulk density as well as narrow particle size distribution so that the polymer may have a reduced amount of untowardly big or minute particles, through a simple process though, is demanded to be developed.
To meet such a need, the present invention hereby intends to provide a method for preparation of a catalyst, which is excellent in its catalytic activity and can help produce a UHMWP having a high bulk density and, a narrow particle size distribution with few untowardly large or small particles; the method can be performed through a simple process by using raw materials of low cost. In addition, the detailed steps or processes for production of the catalyst, provided by the present invention, have never been known in any prior art.
An objective of the present invention is to provide a highly active catalyst for the production of UHMWPE, leading to production of a polymer of high bulk density and such a narrow particle distribution as to evade too large or too small particles.
Another objective is to provide a UHMWPE by a simple yet practical production method and process. Still other objectives and advantages of the present invention will be seen more clearly by referring to the following descriptions and the claims of the present invention.
The catalyst of the present invention for UHMWPE production is characterized by comprising the following, simple yet effective steps: (i) forming a magnesium compound solution by contact-reacting a mixture of a halogenated magnesium compound and an aluminum or a boron compound with alcohol; (ii) reacting the formed magnesium compound solution with an ester compound having at least one hydroxy group and a silicon compound having an alkoxy group; and (iii) producing a solid titanium catalyst by adding a mixture of a titanium compound and a silicon compound thereto.
The kind of halogenated magnesium compounds which can be used in production of the catalyst in the present invention includes: dihalogenated magnesiums such as magnesium chloride, magnesium iodide, magnesium fluoride, or magnesium bromide; alkylmagnesium halides such as methylmagnesium halide, ethylmagnesium halide, propylmagnesium halide, butylmagnesium halide, isobutylmagnesium halide, hexylmagnesium halide, or amylmagnesium halide; alkoxymagnesium halides such as methoxymagnesium halide, ethoxymagnesium halide, isopropoxymagnesium halide, butoxymagnesium halide, or octoxymagnesium halide; and aryloxymagnesium halides such as phenoxymagnesium halide or methylphenoxymagnesium halide. Of the above-named compounds, a mixture of two or more can also be used, and these magnesium compounds can also be effective when they are used in the form of a complex with other metals.
The above-listed magnesium compounds can be represented by simple chemical formulae, but some magnesium compounds can not be represented by simple formula, depending on their manufacturing process. In such cases they generally can be regarded as mixtures of these listed magnesium compounds. For instance, the following compounds can also be used in the present invention: as the compounds obtained by reacting a magnesium compound with a polysiloxane compound, a halogen-containing silane compound, ester, or alcohol; the compounds obtained by reacting a magnesium metal with alcohol, phenol, or ether in the presence of halosilane, phosphor pentachloride, or thionyl chloride. The preferable magnesium compounds are magnesium halides, specifically, magnesium chloride, alkylmagnesium chloride, preferably including alkyl group having the number of 1xcx9c10 carbon atoms, alkoxymagnesium chlorides, preferably including alkoxy group having the number of 1xcx9c10 carbons; aryloxy magnesium chlorides, preferably including aryloxy group having the number of 6xcx9c20 carbons. The magnesium solution used in the present invention can be produced by using the aforesaid magnesium compounds in an alcohol in the presence or absence of a hydrocarbon solvent. The kinds of hydrocarbon solvent which can be used here include, for instance: aliphatic hydrocarbons such as pentane, hexane, heptane, octane, decan or kerosene; alicyclic hydrocarbons such as cyclobenzene, methylcyclobenzene, cyclohexane, or methylcyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, cumene, or cymene; and such halogenated hydrocarbons such as dichloropropane, dichloroethylene, trichloroethylene, carbon tetrachloride, or chlorobenzene.
As for the aluminum compound to be used together with the magnesium compound in the present invention is preferably one or more compounds chosen from the group consisting of: aluminum halides including aluminum fluoride, aluminum bromide, aluminum chloride or aluminum iodide; compounds having a general formula of AlR1n (OR2)3xe2x88x92n, (wherein, R1 is hydrocarbon having 1xcx9c20 carbons or a halogen element, R2 represents hydrocarbon having 1xcx9c20 carbons, and xe2x80x9cnxe2x80x9d means a natural number from 0 to 3) and; mixtures thereof. The compound represented by the general formula AlR1n(OR2)3xe2x88x92n includes, for example aluminum triethoxide, aluminum triisopropoxide, aluminum tributoxide, or aluminum tri-2-ethylhexanoate, etc. can be used.
As for the boron compound to be used together with the magnesium compound in the production of the catalyst in the present invention, one or more compounds selected from a group consisting of boron halides including boron fluoride, boron chloride, or boron bromide; compounds represented by BR1n(OR2)3xe2x88x92n (wherein R1 is a hydrocarbon having 1xcx9c20 carbons or a halogen element, R2 is hydrocarbon having 1xcx9c20 carbons, and xe2x80x9cnxe2x80x9d is a natural number from 0 to 3), and mixtures of these, are preferable. Particularly, the compounds represented by the general formula BR1n(OR2)3xe2x88x92n includes for example, trimethylborate, triethylborate, tributylborate, triphenylborate, methylborondiethoxide, ethylborondiethoxide, ethylborondibutoxide, butylborondibutoxide, boron triethoxide, boron tributoxide, phenylboron diphenoxide, diethylboronethoxide, dibutylboronethoxide, diphenylboronphenoxide, diethoxyboronchloride, diethoxyboronbromide, diphenoxyboronchloride, ethoxyborondichloride, ethoxyborondibromide, butoxyborondichloride, phenoxyborondichloride, ethylethoxyboronchloride, etc. In order to obtain the catalyst effective in producing an UHMWPE of the present invention, having a high bulk density and a narrow particle distribution, the preferred molar ratio of the magnesium compound to the aluminum or boron compound is less than 1:0.25, more preferably 1:0.15.
For the conversion of the magnesium compound into a magnesium solution in the present invention, alcohol is used in the presence of hydrocarbon. The kinds of alcohol used in the process include alcohols having 1xcx9c20 carbons for example, methanol, ethanol, propanol, butanol, pentanol, hexanol, octanol, decanol, dodecanol, octadecylalcohol, benzylalcohol, phenylethylalcohol, isopropylbenzylalcohol, and cumylalcohol, and particularly alcohols having 1xcx9c12 carbons are preferred. Although the desired average size and the particle distribution of the catalyst can vary depending on the kind and the total amount of the alcohol used, and the kind of magnesium compound, the ratio of magnesium to alcohol, etc., but the total amount of the alcohol to obtain the magnesium solution is preferably, at least 0.5 mol, more preferably about 1.0xcx9c20 mols, still preferably about 2.0xcx9c10 mols per 1 mol of the magnesium compound. The reaction of the magnesium and the alcohol for the production of the magnesium compound solution is preferably performed in a hydrocarbon medium, the temperature preferably, though depending on the kinds and amount of the alcohol, being at about xe2x88x9225xc2x0 C., preferably xe2x88x9210xcx9c200xc2x0 C., and more preferably about 0xcx9c150xc2x0 C., for about 15 minutes xcx9c5 hours, preferably about 30 minutes xcx9c4 hours.
As for the ester compound to be used in the present invention as an electron donor, may includes the followings, for example: unsaturated fatty acid esters containing at least one hydroxy group such as 2-hydroxy ethylacrylate, 2-hydroxy ethylmethacrylate, 2-hydroxy propylacrylate, 2-hydroxy propylmethacrylate, 4-hydroxy butylacrylate, or pentaerythritol triacrylate; aliphatic monoesters or polyesters containing at least one hydroxy group such as 2-hydroxy ethylacetate, methyl 3-hydroxy butyrate, ethyl 3-hydroxy butyrate, methyl 2-hydroxy isobutyrate, ethyl 2-hydoxy isobutyrate, methyl-3-hydroxy-2-methyl propionate, 2,2-dimethyl-3-hydroxy propionate, ethyl-6-hydroxy hexanoate, t-butyl-2-hydroxy isobutyrate, diethyl-3-hydroxy glutarate, ethyl lactate, isopropyl lactate, butylisobutyl lactate, isobutyl lactate, ethylmandelate, dimethyl ethyl tartrate, ethyl tartrate, dibutyl tartrate, diethyl citrate, triethyl citrate, ethyl 2-hydroxy caproate, or diethyl bis-(hydroxy methyl) malonate; aromatic esters containing at least one hydroxy group such as 2-hydroxy ethyl benzoate, 2-hydroxy ethyl salicylate, methyl 4-(hydroxy methyl) benzoate, methyl 4-hydroxy benzoate, ethyl 3-hydroxy benzoate, 4-methyl salicylate, ethyl salicylate, phenyl salicylate, propyl 4-hydroxy benzoate, phenyl 3-hydroxy naphthenoate, monoethylene glycol monobenzoate, diethylene glycol monobenzoate, triethylene glycol monobenzoate, etc. and; alicyclic esters containing at least one hydroxy group such as hydroxy butyl lactone. In order to obtain the catalyst effectively leading to the production of a UHMWPE having a high bulk density, a narrow particle distribution to obviate too large and small particles, the amount of the ester compound containing at least one hydroxy group should be 0.001xcx9c5 mols to a mol of magnesium, preferably 0.01xcx9c2 mols.
As for the silicon compound having an alkoxy group, which can be used as another electron donor in the present invention, a compound which is represented by the general formula: RnSi(ORxe2x80x2)4xe2x88x92n (wherein R and Rxe2x80x2 are hydrocarbons having 1xcx9c12 carbons, and xe2x80x9cnxe2x80x9d is a natural number from 1 to 3) is preferred. In particular, compounds such as dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, methylphenylmethoxysilane, diphenyldiethoxysilane, ethyltrimethoxysilane, vinyltrimethoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, methyltrimethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, butyltriethoxysilane, phenyltriethoxysilane, ethyltriisopropoxysilane, vinyltributoxysilane, ethylsilicate, butylsilicate, methyltriaryloxysilane can be used. In order to obtain the catalyst for production of an UHMWPE having a high bulk density and a narrow particle size distribution provided by the present invention, the amount of the above-said silicon compound having an alkoxy group should preferably be in the ratio of 0.05xcx9c3 mols to a mol of the magnesium, more preferably the ratio 0.1xcx9c2 mols. The temperature for the reaction of the liquid magnesium compound solution with an ester compound containing at least one hydroxy group and an alkoxy silicon compound is preferably 0xcx9c100xc2x0 C., or more preferably 10xcx9c70xc2x0 C.
For the catalyst in the present invention, the magnesium compound solution which has been reacted with an ester compound containing at least one hydroxy group and an alkoxy silicon compound is afterwards reacted with a liquid titanium compound represented by the general formula Ti(OR)aX4xe2x88x92a (wherein R is a hydrocarbon, X is a halogen atom, xe2x80x9caxe2x80x9d is a natural number 0xe2x89xa6axe2x89xa64) and a silicon compound represented by the general formula Rn, SiCl4xe2x88x92n (wherein R is a hydrocarbon, xe2x80x9cnxe2x80x9d is a natural number 0xe2x89xa6nxe2x89xa64), to form a catalyst particles. Of the above general formulae, R represents an alkyl group having the number of 1xcx9c10 carbon atoms.
The kind of titanium compounds which satisfy the above general formula Ti(OR)aX 4xe2x88x92a includes, for example, tetra-halogenated titaniums such as TiCl4, TiBr4, and TiI4; tri-halogenated alkoxy titaniums such as Ti(OCH3)Cl3, Ti(OC2H5)Cl3, Ti(OC2H5)Br3, and Ti(O(ixe2x88x92C4 H9)Br3; dihalogenated alkoxy titaniums such as Ti(OCH3)2Cl2, Ti(OC2H5)2Cl2. Ti(O(ixe2x88x92C4H9))2Cl2, and Ti(OC2H5)2Br2; and tetraalkoxy titaniums such as Ti(OCH3)4, Ti(OC2H5)4, and Ti(OC4H9)4. Mixtures of the above titanium compounds can also be used in the present invention. The preferred titanium compounds are halogen-containing compounds, and more preferred one is titanium tetrachloride.
The kind of silicon compounds which satisfy the above general formula RnSiCl4xe2x88x92n, include, for example: tetrachlorosilicon; trichlorosilanes such as methyltrichlorosilane, ethyltrichlorosilane, and phenyltrichlorosilane; dichlorosilanes such as dimethyldichlorosilane, diethyldichlorosilane, diphenyldichlorosilane, and methylphenyldichlorosilane; and a monochlorosilane such as trimethylchlorosilane. The mixtures of these silicon compounds can also be used. The preferred silicon compound is silicon tetrachloride.
In order to obtain the catalyst effectively leading to the production of a UHMWPE with a high bulk density and a narrow particle size distribution, the amount of the mixture of a titanium compound and a silicon compound suitable for the formation of the catalyst particles is preferably 0.1xcx9c200 mols to a mol of the magnesium compound, preferably 0.1xcx9c100 mols, and more preferably 0.2xcx9c80 mols. The ratio of titanium compound to silicon compound in the mixture is preferably 1:0.05xcx9c0.95, or more preferably 1:1xcx9c0.8.
The shape and size of the solid catalyst component in the present invention may greatly vary depending on the condition of the reaction where the magnesium compound solution reacts with the mixture of titanium and silicon compounds. Therefore, the reaction of the magnesium compound solution with the mixture of titanium and silicon compounds is carried out at a sufficiently low temperature for the formation of solid components. Preferably, the contact reaction is carried out at xe2x88x9270xc2x0 C.xcx9c70xc2x0 C., and more preferably at xe2x88x9250xc2x0 C.xcx9c50xc2x0 C. After the contact reaction, the temperature is slowly raised and maintained at 50xc2x0 C.xcx9c150xc2x0 C. for 30 minutes xcx9c5 hours for sufficient reaction.
The solid catalyst particles obtained by the above-said reaction can be further reacted with a titanium compound. The titanium compound for this purpose is a titanium halide or a halogenated alkoxy titanium having 1xcx9c20 carbons of an alkoxy group. In some cases mixtures of these can also be used. Of these, a titanium halide or a halogenated alkoxy titanium having 1xcx9c8 carbons of an alkoxy group is preferred, and titanium tetrahalide is still more preferred.
The solid complex titanium catalyst produced by the method provided by the present invention is advantageously used in polymerization and copolymerization of ethylene. In especial, this catalyst is preferably used in polymerization of ethylene and also in copolymerization of ethylene with xcex1-olefins containing three or more carbons such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, and 1-hexene.
The polymerization reaction in the presence of the catalyst of the present invention is performed with the use of (i) the solid complex titanium catalyst of the present invention consisting of magnesium, titanium, halogen and an electron donor, and (ii) the organometalic compounds of Groups II and III in the periodic table.
The solid complex titanium catalyst of the present invention can also be pre-polymerized with ethylene or xcex1-olefin, before being used in a polymerization reaction as a component. The pre-polymerization can be performed in the presence of the afore-said catalyst components, an organic aluminum compound such as triethylaluminum, and a hydrocarbon solvent like hexane, under the pressure conditions of ethylene or xcex1-olefin at sufficiently low temperature. Pre-polymerization makes catalyst particles wrapped in polymers to maintain the shape of the catalyst, and thus helps to better the shape of the polymer after the polymerization. The ratio in weight of polymer to catalyst after the pre-polymerization is usually 0.1:1xcx9c20:1.
The organometalic compound useful in the present invention can be represented by the general formula MRn, wherein M stands for metals of Groups II or IIIA in the periodic table such as magnesium, calcium, zinc, boron, aluminum or potassium; xe2x80x9cRxe2x80x9d for alkali groups having 1xcx9c20 carbons such as methyl, ethyl, butyl, hexyl, octyl, and decyl; xe2x80x9cnxe2x80x9d for the atomic valence of metal atom. The example of the more preferred organometalic compounds include trialkylaluminums containing an alkyl group of 1xcx9csix carbons such as triethylaluminum and tri-isobutylaluminum and mixtures thereof. In some cases, organic aluminum compounds containing one or more halogen or hydride groups for example ethylaluminum dichloride, diethylaluminum chloride, ethylaluminum sesquichloride, and diisobutylaluminum hydride can be used. Mixtures of these organometalic compounds can also be used.
The polymerization reaction in the present invention is performed in the gas phase or in bulk in the absence of an organic solvent, or carried out in liquid slurry in the presence of an organic solution. These reactions, however, are performed in the absence of oxygen, water, or any compounds that may act as a catalytic poison. In the case of liquid slurry polymerization, the suitable concentration of the solid complex titanium catalyst (i); in the polymerization reaction system, is about 0.001xcx9c5 mmols, more preferably about 0.001xcx9c0.5 mmols in terms of the titanium atoms of the catalyst to one liter of the solvent. As for the solvent, alkanes and cycloalkanes such as pentane, hexane, heptane, n-octane, isooctane, cyclohexane, and methylcyclohexane; alkylaromatics such as toluene, xylene, ethylbenzene, isopropylbenzene, ethyltoluene, n-propylbenzene, and diethylbenzene; halogenated aromatics such as chlorobenzene, chloronaphthalene, and ortho-dichlorobenzene; and mixtures thereof, can be useful. In the case of gas phase polymerization, the amount of the solid complex titanium catalyst (i) is about 0.001xcx9c5 mmols, preferably about 0.001xcx9c1.0 mmols, still preferably about 0.01xcx9c0.5 mmols in terms of the titanium atoms in the catalyst to a liter of the polymerization reactor volume. The preferable concentration of the organometalic compound (ii) is about 1xcx9c2000 mols to a mol of the titanium atoms in the catalyst (i), more preferably about 5xcx9c500 mols, calculated by the organometalic atoms. That the concentration and amount of the solid complex catalyst are specified as above is to obtain a polymer having a large bulk density and a narrow particle distribution to admit the least possible amount of too large and small particles.
To secure a high polymerization rate the reaction is performed at a sufficiently high temperature regardless of the polymerization process itself. Generally, approximately 20xcx9c200xc2x0 C. are preferred, and more preferably 20xcx9c95xc2x0 C. The pressure of a monomer during polymerization is adequately the atmospheric xcx9c100, and more preferably 2xcx9c50 psi.